Catalytic chain transfer is an effective way to control the molecular weight of polymers of methacrylates and styrenes. It is known that chain transfer catalysis (CTC) products contain a terminal vinylidene bond. This feature makes these products attractive as macromonomers for a variety of applications. However, CTC has not been known to be applicable for reduction of molecular weight in the polymerizations of other vinylic monomers such as acrylates.
Copolymerizations of methacrylate monomers with monosubstituted monomers in the presence of cobalt have been described in the art. However, the monosubstituted monomer is almost always present as a minor component. U.S. Pat. No. 4,680,354 describes molecular weight reduction using various Co(II) complexes in MMA-BA, MMA-EA and MMA-BA-St copolymerizations, wherein the abbreviations represent:
MMA=methyl methacrylate
BA=butyl acrylate
EA=ethyl acrylate
St=styrene.
U.S. Pat. No. 5,324,879 describes molecular weight reduction with Co(III) complexes in EA, St, and vinyl acetate (VAc) polymerizations, and MMA-EA copolymerization.
U.S. Pat. No. 4,680,352 describes molecular weight reduction and macromonomer (polymers or copolymers with unsaturated end-groups) synthesis in copolymerizations with acrylates and styrene with various Co(II) complexes. Various terpolymerizations are cited therein; however, no evidence of the nature or existence of terminal double bonds is given.
Gruel et al., Polymer Preprints, 1991, 32, p. 545, reports the use of Co(II) cobaloximes in low conversion St-MMA copolymerizations at low temperatures with end group analysis.
The references cited above cover the copolymerization of acrylates and styrene with methacrylate monomers, but do not disclose synthetic conditions for production of high purity macromonomers based on acrylates and styrene, nor branching of the resulting products. The conditions disclosed are unlikely to yield high purity macromonomers for systems composed predominantly of monosubstituted monomers. Disclosed temperatures of less than 80° C. are likely to provide substantial amounts of undesired graft copolymer at high conversion rates.